you can hit it in whatever mode you want...if you are rolling and want to have some fun..just kick the switch...orrr do it old fashion, use the paddle shifters and drop 2-3 gears depending on your speed...and go crazy with the paddle
though if you are in 2nd and you hit the switch, it wouldn't be different from not hitting it..because you are already at lowest gear..
welll as far as i know...when you start pressing on the paddle, you will reach a point where it feels like there is a solid rock under the paddle and needs a little more effort to let the paddle go any farther..that's your kickdown switch!
if you press the kickdown switch, by flooring it all the way to your carpet..the car will downshift to the lowest gear possible without damaging anything, so you can be have maximum acceleration..
say you are in 6th gear, like where you usually are in D mode...you hit the KD switch, it would take you to 3rd gear, depending on your speed, and push you back in the seat...if you don't hit the switch, it would take you to maybe 5th and go all the way to redline normally...
so why people don't like the switch? well because it takes time aka delay..for it to does it's job and take you to lowest gear, which is bad if you are racing someone.